No abstract

Single-atom electrocatalysts (SAEs) can realize the target of low-cost by maximum atomic efficiency. However, they usually suffer performance decay due to high energy states, especially in a harsh acidic water splitting environment. Here, we conceive and realize a double protecting strategy that ensures robust acidic water splitting on Ir SAEs by dispersing Ir atoms in/onto Fe nanoparticles and embedding IrFe nanoparticles into nitrogen-doped carbon nanotubes (Ir-SA@Fe@NCNT). When Ir-SA@Fe@NCNT acts as a bifunctional electrocatalyst at ultralow Ir loading of 1.14 μg cm −2 , the required overpotentials to deliver 10 mA cm −2 are 250 and 26 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 0.5 M H 2 SO 4 electrolyte corresponding to 1370-and 61-fold better mass activities than benchmark IrO 2 and Pt/C at an overpotential of 270 mV, respectively, resulting in only 1.51 V to drive overall water splitting. Moreover, remarkable stability is also observed compared to Pt/ C-IrO 2 .

Evaporation of droplets over a hot oil surface is a natural phenomenon. However, most existing studies focus on a single droplet, and the evaporation of multiple droplets is insufficiently understood. Here, we explore the Leidenfrost evaporation of two identical FC-72 droplets over a hot oil bath. The oil temperature covers 73.6~126.6 ^°C, and the evaporation of droplets with an initial diameter of 1.5 mm was recorded by an infrared thermographer and a high-speed camera. The shallow oil depth keeps a relatively uniform oil temperature in the slot compared to the deep liquid pool, due to the larger ratio of the surface area for copper-oil contact to the slot volume. We found that neighboring droplets evaporate in three stages: non-coalescence, bouncing and separation. The radius of neighboring Leidenfrost droplets follows the power law <em>R</em>(<em>t</em>)~(1−<em>t</em>/<em>τ</em>)<em>ⁿ</em>, where <em>τ</em> is the characteristic droplet lifetime and <em>n</em> is an exponent factor. Moreover, the diffusion-mediated interactions between the neighboring droplets slow down the evaporation process compared to isolated Leidenfrost droplets and lead to an asymmetric temperature field on the droplet surface, which breaking the balance of the forces acting on the droplets. A simple dual-droplet evaporation model is developed which considers four forces acting horizontally on the droplet, including the Marangoni force resulting from the non-uniform droplet temperature, the gravity component, the lubrication-propulsion force, and the viscous drag force. Scale analysis shows that the Marangoni force and gravity component dominate dual-droplet evaporation dynamics. In the non-coalescence stage, the gravity component induces the droplets to attract each other, while the vapor film trapped between droplets avoids their direct touch. When the droplets get smaller, the gravity component is insufficient to overcome the Marangoni force. Hence, the droplets separate in the final evaporation stage. Finally, we identify the competition between Marangoni force and gravitational force as the origin of the bounce evaporation by comparing the theoretical and experimental transition times at distinct stages. This study contributes to explaining the complex Leidenfrost droplet dynamics and evaporation mechanism.

Molecular dynamics (MD) simulation is a powerful tool to investigate the nanoscale fluid flow. In this article, we review the methods and the applications of MD simulation in liquid flows in nanochannels. For pressuredriven flows, we focus on the fundamental research and the rationality of the model hypotheses. For electrokineticdriven flows and the thermal-driven flows, we concentrate on the principle of generating liquid motion. The slip boundary condition is one of the marked differences between the macro-and micro-scale flows and the nanoscale flows. In this article, we review the parameters controlling the degree of boundary slip and the new findings. MD simulation is based on the Newton's second law to simulate the particles' interactions and consists of several important processing methods, such as the thermal wall model, the cut-off radius, and the initial condition. Therefore, we also reviewed the recent improvement in these key methods to make the MD simulation more rational and efficient. Finally, we summarized the important discoveries in this research field and proposed some worthwhile future research directions.

No abstract